I’ve upset a friend. Advice?

A few days ago I stayed at a very close friends house. We’ve been friends for 4+ years, both her and her husband are close friends of mine. We hung out as usual and then myself and the wife were tried so we went inside, she went to bed and the bed I was supposed to be sleeping on was out on the lounge room floor and the husband was lying on it watching tv, I sat on the couch for a while but it was really uncomfortable so I asked him if it was okay if I got onto the bed and laid in the opposite way (so his feet were at my head) we watched an episode and he went to bed, we were fully clothed, not touching. I didn’t even think anything of it, I’d never in a million years consider doing anything that made them uncomfortable. I got a message from my friend last night saying she was really upset that I climbed into bed with her husband and doesn’t want to speak to me for a while.

I’m really upset by this because I never ever intended to upset her and I feel stupid that I didn’t realise at the time that it might make her uncomfortable, I saw it the same as if we were both sitting on the couch. I don’t know what to do, I feel awful, I don’t want to lose two of my closest friends and I don’t know how to make it right. Any advice would be greatly appreciated